1. Field of the Invention
The present invention relates generally to wireless communications and, more particularly, to a Random Access CHannel (RACH)-related system resource optimization method and apparatus in a wireless communication system.
2. Description of the Related Art
Long Term Evolution (LTE), which is a project to improve the Universal Mobile Telecommunication Standard (UMTS), is a next generation high-speed wireless communication technology based on Orthogonal Frequency Division Multiplexing (OFDM).
FIG. 1 is a diagram illustrating an LTE system architecture.
As shown in FIG. 1, the LTE mobile communication is characterized with Evolved Radio Access Networks (E-RANs) 110 and 112 having only two infrastructure nodes: Evolved Node B′s (ENBs) 120, 122, 124, 126, and 128 and anchor nodes 130 and 132. A User Equipment (UE) 101 accesses an Internet Protocol (IP) network 114 via E-RANs 110 and 112. The ENBs 120, 122, 124, 126, and 128 are responsible for wireless channel establishment for the UE 101 and management of the cells and wireless resources. For example, the ENBs 120, 122, 124, 126, and 128 broadcast system information, allocate a radio resource for transmission of data and control information to the UE 101, and determine a handover of the UE 101 based on the channel management information collected from the current cell and its neighbor cells. The ENBs 120, 122, 124, 126, and 128 are provided with a control protocol such as a Radio Resource Control (RRC) protocol related to the radio resource management.
FIG. 2 is a diagram illustrating an LTE system including a Self Optimized Network (SON) server.
In the LTE system of FIG. 1, the SON is the network which optimizes the parameters related to the system resources of a cell automatically. Specifically, the network optimizes the system resource-related parameters automatically based on the statistical values reported by a UE 201 and/or obtained through self-management operations without any network test by operator personnel. The UE 201 and an ENB 211 communicate data and control information through a radio interface. An SON server 221 receives the statistical values from the ENB 211 and determines policies suitable for the ENB 211 and the parameter values related to the system information of the cell. Some parameters related to the system resources can be optimized automatically within the ENB 211 without involvement of the SON server 221.
FIG. 3 is a signaling diagram illustrating RACH signaling between a UE and an ENB in a conventional LTE system. In FIG. 3, a UE 301 can access the RACH of an ENB 303 defining a specific cell. The UE 301 selects a preamble group and transmits a code sequence, specifically a random access preamble, selected from the preamble group to the ENB 302 on the predetermined RACH resource in step 311. How to select the preamble group follows the 3GPP standard TS36.321v8.4.0. Typically the preamble group is selected based on the current channel condition and the size of a message to be transmitted. If the random access preamble has been received, the ENB 303 transmits a random access response containing preamble ID information, Timing Advance (TA) information for adjusting uplink timing, uplink resource allocation information for transmitting a message, and Temporary Radio Network Temporary Identifier (T-RNTI) in step 321. The ENB 303 can allocate different uplink resource depending on the preamble group to which the random access preamble belongs. For example, if a parameter messageSizeGroupA having the value of b56 is broadcast as the system information, and if the received preamble belongs to the preamble group A, the uplink resource is allocated as much as 56 bits. Otherwise, if the received preamble belongs to the preamble group B, the uplink resource can be allocated as much as more than 56 bits.
If the random access response message has been received, the UE 301 transmits a scheduled transmission message to the ENB 303 using the uplink resource in step 331. At this time, if the preamble received at step 321 matches the preamble transmitted at the UE 301, the UE 301 transmits an L2/L3 message. When multiple UEs have transmitted the random access preambles simultaneously, the preambles can collide at step 311. In order to clearly acknowledge the receipt of the preamble, the ENB 303 transmits a contention resolution message containing a Serving Temporary Mobile Subscriber Identity (S-TMSI) or the random identity information to the UE 301 in step 341. Each of the UEs that transmitted the same preamble receives the contention resolution message and checks whether the S-TMSI or the random identity information contained in the contention resolution message is identical with that transmitted in the scheduled transmission message. If the received identity information matches the received identity information, the UE continues the RACH procedure. If the received identity information does not match the received identity information, the UE reinitiates the RACH procedure.
Table 1 shows the Medium Access Control (MAC) system parameters broadcast in association with the RACH procedure in the LTE system. Reference is made to the 3GPP standards TS36.331v8.4.0 and TS36.321v8.4.0 specifying the parameters listed in Table 1.
TABLE 1RACH-ConfigCommonpreambleInfo> numberOfRA-PreamblesENUM {n4, n8, n12, n16, n20,n24, n28, n32, n36, n40, n44, n48,n52, n56, n60,> preamblesGroupAConfig>> sizeOfRA-PreamblesGroupAENUM {n4, n8, n12, n16, n20,n24, n28, n32, n36, n40, n44, n48,n52, n56, n60,>> messageSizeGroupAENUM {b56, b144, b208, spare1}>> messagePowerOffsetGroupBENUM {minusinfinity, spare1}powerRampingParameters> powerRampingStepENUM {dB0, dB2, dB4, dB6}>ENUM {dBm-120, dBm-118,preambleInitialReceivedTargetPowerdBm-116, dBm-114, dBm-112,dBm-110, dBm-108, dBm-106,dBm-104, dBm-102, dBm-100,dBm-98, dBm-96, dBm-94,dBm-92,ra-SupervisionInfo> preambleTransMaxENUM {n3, n4, n5, n6, n7, n8,n10, n20, n50, n100, n200, spare5,spare4, spare3, spare2, spare1}> ra-ResponseWindowSizeENUM {sf2, sf3, sf4, sf5, sf6,sf7, sf8, sf10}> mac-ENUM {sf8, sf16, sf24, sf32, sf40,ContentionResolutionTimersf48, sf56, sf64}maxHARQ-Msg3TxINT (1 . . . 8)
Among the RACH MAC parameters, messageSizeGroupA represents the transmission message size parameters as the references for selecting the preamble group. For example, if the mesageSizeGroupA is set to b56 and if the uplink message size is shorter than 56 bits, the preamble group A is selected.